Overbank Flow from a Sinuous Submarine Channel: Process and Product

Kane, Ian¹, William. D. McCaffrey¹, Jeff Peakall¹ (1) University of Leeds, Leeds, United Kingdom

Key differences between flow in subaerial and submarine channels are 1) the absence of a free upper surface 2) a reduced density difference between flow and ambient fluid and 3) the nature of overbank flow. Super-elevated flow spilling from the channel builds levees through deposition of sediment. This levee growth has implications for the downstream evolution of, and deposition from, the within channel flow. Here we report detailed experiments which examine this process. A series of experiments were run in a tank 1.7 m2 and 1.5 m deep, with an inlet channel centered on one face. An ‘incised' channel was cut out of acrylic sheets of varying thickness so that the channel depth could be systematically altered. Suspensions of mixed grain-size sediment (glass ballotini and silica flour) were mixed in a 10 liter lock box and rapidly released. Ultrasonic velocity profiling and siphon sampling were used to measure flow velocities and sediment concentrations respectively. Post-flow sediment distributions were accurately mapped. Flows were observed to follow the curved channel with very little overspill, even in cases where the mean flow height was more than twice that of the levees. The degree of overspill is quantified as a function of sediment stratification. Comparison is made between experimental overbank deposits and data from an ancient system, the Cretaceous Rosario Fm., Baja California, Mexico.